It is known that corrosion is a problem in aqueous fluids utilized for the working of metals. Corrosion inhibitors are commonly added to aqueous fluids to mitigate corrosion of ferrous metals. Typical examples of corrosion inhibitors known in the art are zinc chromate, dithiophosphates, metal sulfonates, alkanolamines, alkyl amines, borate compounds, carboxylic acids including polyaspartic acid at high pH (10 and above), alkyl amidocarboxylic acids, sodium molybdate, boric acid with various ethanol amines, benzoic acid and nitro derivatives thereof, ammonium benzoate, triethanolamine salts of carboxylic acids with a carboxymethyl thio group, tungstates, phosphates, polyphosphates, phosphonates, nitrates and silicates.
U.S. Pat. No. 5,723,061 discloses an antifreeze composition containing a corrosion inhibitor system comprising a mixture of at least two aromatic or aliphatic dicarboxylic acids or alkali metal, ammonium or amine salts thereof, at least one 1,3-diazole chosen from imidazole, benzimidazole, imidazoline and the hydrocarbon derivatives thereof, and at least one triazole compound such as benzotriazole, tolyltriazole, or N-substituted derivatives thereof. The '061 patent also states that GB-1,004,259 discloses a corrosion inhibitor composition comprising a mixture of benzotriazole and/or methylbenzotriazole and an alkali metal, ammonium, amine or alkanolamine salt of a C.sub.6 to C.sub.30 saturated dicarboxylic acid.
WO 96/39549 discloses corrosion inhibiting formulations for use in closed water systems comprising at least one water soluble fatty acid salt of the formula R.sup.1 (COOX).sub.n wherein R.sup.1 is alkyl or hydroxyalkyl having at least 2 carbon atoms, preferably 2-18 carbon atoms, and n is 2 or 3, and optionally at least one additive which may be a corrosion inhibitor, selected from the group of alkali metal borates, alkali metal molybdates, hydrocarbyl triazoles, silicates, morpholine, ethylenediamine, pyridine and pyrrolidine.
U.S. Pat. No. 3,945,931 discloses an aqueous metal working fluid containing amido acids of the formula ##STR1##
wherein R is an open chain aliphatic hydrocarbon group having between 9 and 25 carbon atoms, and n and n' are whole numbers or zero, the same or not, the sum of n and n' being equal to 1 or 2. The fluids of the '931 patent optionally contain salts of phosphoric esters, as well as other additives such as anti-foam agents, bactericides and anti-corrosive agents. The anti-corrosive agents can be alkaline nitrates, phosphates, borates, etc.
U.S. Pat. No. 5,599,779 discloses synergistic rust inhibitor compositions consisting of N-acyl sarcosines of the formula ##STR2##
wherein R represents alkyl or alkenyl group of 8-18 carbon atoms, a dicarboxylic acid of the formula HOOC(CH.sub.2).sub.x COOH wherein x is an integer from 4 to 46, and an amine selected from a primary, secondary or tertiary alkyl amine or an imidazoline, and the molar ratio of sarcosine to dicarboxylic acid to amine is about 2:1:2 to 7:1:2.
While amido acids have been disclosed for use in aqueous metal working fluids and triazoles have been disclosed as corrosion inhibitors in aqueous compositions, it has now been surprisingly discovered that the amido acids or salts thereof of the invention produce a synergistic corrosion inhibiting effect in aqueous compositions, particularly aqueous metal working compositions, when combined in specific proportions with the aryltriazoles or 3-amino-1,2,4-triazole of the invention.